To look at the owners manual for this unit but what is required here is to Switch the Monitor to the External Monitor from the internal one. So plug in the Monitor/Projector and then with the specified Key Combination press the keys and it will switch to the external Display.

If you don't have a Owners Manual you can download one from the Dell Web Site when it's back up to find out the Key Combination that this unit requires. Of course if the Adapter Lead has drivers with it you'll need to install those first.